The present invention relates to a liquid ejecting apparatus equipped with a liquid ejecting head from which liquid droplets are ejected through nozzle openings by pressurizing a pressure generating chamber using pressure generator.
A summary of a driving method of a related liquid ejecting head in an inkjet serial printer system as an example of a liquid ejecting apparatus will now be described with reference to the accompanying drawings.
FIG. 1 is a view showing a relation between a liquid ejecting apparatus main body (hereinafter, referred to as the main body) 1 and a liquid ejecting head. The main body 1 performs information processing and supplies driving power to the liquid ejecting head 2 as a subject to be controlled. The main body 1 includes a control circuit 3 that creates data used to determine nozzle(s) which ejects liquid droplets and provides timing, a driving signal generating circuit 4 that generates a driving signal for driving actuators (9 through 11) of the liquid ejecting head 2, transistors 5 and 6 that amplify the driving signal generated in the driving signal generating circuit 4, and a connector 7 that outputs control data and driving power to the liquid ejecting head 2. The liquid ejecting head 2 includes a connector 8 into which a driving signal waveform from the driving signal generating circuit 4 is inputted, a plurality of actuators 9 through 11 having piezoelectric vibrators that generate kinetic energy needed to eject liquid droplets, analog switches 12 through 14 that control the driving signal waveform from the actuator main bodies, and a control circuit 15 that controls vibrations of the actuators 9 through 11 through ON/OFF operations of the analog switches 12 through 14 according to data from the control circuit 3 in the main body 1. The liquid ejecting head 2 reciprocates on the guide within a liquid ejecting apparatus mechanism, and receives data corresponding to the position on the guide from the main body 1, whereupon it ejects liquid droplets and hence performs printing. The main body 1 and the ejecting head 2 are connected to each other through a flexible flat cable (hereinafter, abbreviated to FFC) 16. As shown in FIG. 2, the FFC 16 is shaped like a strip, including a number of conducting lines used as conduction patterns 17 that are aligned in parallel to one another and molded in synthetic resin 18 having good flexibility and durability to withstand bending deformation so as not to interfere with reciprocating motions of the liquid ejecting head 2. In order to provide the conducting patterns 17 per se with the same durability as that of the synthetic resin 18, the conduction patterns 17 include a thin-plate member made of copper alloy, patterned into narrow slips.
The conduction patterns 17 are formed of driving signal lines of the piezoelectric vibrators, earth lines, temperature-detecting signal lines, other driving power supply lines, etc., which are determined by the number of kinds of liquid. Recently, in order to meet the need to improve a printing quality or the like, not only the kinds of liquid, but also the kinds of signals to be inputted into the liquid ejecting head 2 from the driving signal generating circuit 4 have to be increased, so that the liquid ejecting apparatus adapts to the environments, such as temperature and humidity, at a site where a recording apparatus is installed.
Meanwhile, a liquid ejecting head 2 and a liquid ejecting apparatus that comply not only with a conventional consumer apparatus (A-size), but also with an apparatus for large format printer (hereinafter, abbreviated to LFP) of an A0/B0 size have now become commercially available with the expansion in application of the liquid ejecting apparatus, and the FFC 16 is correspondingly increased in length.
The FFC 16 almost two times longer than a moving span of the liquid ejecting head 2 is used so as not to interfere with smooth reciprocating motions of the liquid ejecting head 2. However, there are parasitic impedance components that are proportional to the length of the FFC 16. Because the liquid ejecting head 2 in the LFP naturally increases in width in the main scanning direction, the FFC 16 is extended as long as approximately 4 m and impedance components are correspondingly increased, which is schematically shown in FIG. 3. In the drawing, numeral 19 denotes a variable capacitance representing the analog switches 12 through 14 and the actuators 9 through 11 of FIG. 1, numerals 20 and 21 denote parasitic inductance components, and numerals 48 and 49 denote parasitic resistance components, each of which is present in the conduction patterns 17 of FIG. 1. The inductance components give rise to a back electromotive force that is proportional to differentiation of a current flowing through the FFC 16 with respect to time. However, when a quantity of the current increases, so does the differentiation of the current with respect to time. Thus, when a capacitance load increases, so does the back electromotive force in magnitude. Accordingly, when the FFC 16 is increased in length, as shown in FIG. 4A, there occurs a phenomenon that discrepancy is caused between a driving signal waveform in the vicinity of the emitters of the transistors 5 and 6 in the main body 1 and a driving signal waveform across the variable capacitance 19. This raises a problem that the driving voltage specified in driving voltage information ID is not applied to the piezoelectric vibrators. In particular, because the inductance components give rise to an overshoot and an undershoot of a voltage in the ejecting head 2, a driving voltage substantially higher than a voltage appropriate for driving the piezoelectric vibrators is applied. Values larger than appropriate values are thus given to a liquid droplet ejecting speed and a discharged liquid droplet weight. This means that the position and the size of a dot formed on the surface of a sheet of paper through discharge differ with the number of nozzles from which liquid droplets are ejected for one pulse, and the printing quality is adversely influenced.
On the other hand, as shown in FIG. 4B, the resistance components of the FFC 16 become a factor that causes a voltage drop and a delay in response when the piezoelectric vibrators are charged and discharged. When a current flowing through the FFC 16 increases, a voltage on the variable capacitance 19 side drops, and contrary to the inductance components, the piezoelectric vibrators are driven on a voltage substantially lower than the driving voltage specified in the driving voltage information ID. Values smaller than appropriate values are thus given to a liquid droplet ejecting speed and an ejected liquid droplet weight. Also, in the case of printing at a printing quality as high as a picture quality, a liquid droplet weight per dot needs to be reduced to approximately 5 ng. However, for such a minute liquid droplet to be ejected, it becomes essentially necessary to drive the piezoelectric vibrators to cause displacement at a higher speed than in the case of ejecting a related large liquid droplet (10 to 40 ng). To displace the piezoelectric vibrators at a high speed, a charging and discharging time of a driving signal has to be shortened, and naturally a change rate with respect to time and an absolute value of a current are increased, which in turn increases distortion due to the impedance components of the FFC 16. The impedance components of the FFC 16 need to be reduced as small as possible to solve such a problem. However, there is a limit to a reduction of the impedance components because of the restriction of a conducting line width and a length of the FFC 16. It should be noted that, as a matter of course, it is impossible to shorten the FFC 16 in the LFP, and increasing the conducting line width or the number of cores of the FFC 16 results in an increase of the cost of the liquid ejecting apparatus main body 1.